<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <style>
        *{
            padding: 0;
            margin: 0;
            box-sizing: border-box;
        }
        .container {
            width: 500px;
            height: 500px;
            background-color: blue;
            padding: 20px;      
        }
        .container .childern {
            width: 200px;
            height: 200px;

            background-color: brown;

        }
    </style>
    <div class="container">

        <div class="childern">

        </div>
    </div>
</body>
</html>